Process for producing composite material comprising resin molded product

ABSTRACT

The present invention provides a method for allowing a metal complex to stably penetrate into a polymer and immobilizing the metal complex in the polymer by a low temperature treatment, in a batch processing for a plating pre-treatment wherein the metal complex is allowed to penetrate into the polymer with the use of high-pressure carbon dioxide. In particular, the present invention provides a method for producing a composite material containing a resin molded product, characterized in that a reducing agent is brought into contact with the resin molded product so as to allow the reducing agent to penetrate into the resin molded product, and in that high-pressure carbon dioxide having an organic metal complex dissolved therein is brought into contact with the resin molded product into which said reducing agent has penetrated, so as to immobilize the organic metal complex in the resin molded product by the reducing agent.

TECHNICAL FIELD

The present patent application is filed claiming the priority of the Japanese patent application No. 2008-62767 (filed on Mar. 12, 2008) of which the entire content is incorporated in the present patent application by reference thereto.

The present invention relates to a method for producing a composite material containing a resin molded product.

BACKGROUND OF THE INVENTION

Electorless plating is a conventionally known method for forming a metal film on a resin molded product such as a polymer member (i.e., a polymer molded product) at lower cost. In the electroless plating, to ensure adhesion of a plating film, an oxidizing agent such as a hexavalent chromic acid, permanganic acid or the like is used to etch the surface of the polymer member as a pre-treatment for electroless plating, to thereby roughen the surface of the polymer member. However, the use of the oxidizing agent such as hexavalent chromic acid or permanganic acid gives a large burden on the environment.

Selection of a polymer to be dipped in such an etching solution, i.e., a polymer applicable to electroless plating, is limited to a part of polymers such as ABS, etc. This is because the ABS contains a butadiene rubber component into which an etching solution selectively penetrates to roughen the surface of a polymer member, while other polymer materials contain only bits of components to be selectively oxidized by such an etching solution, with the result that obtained polymer members are hard to be roughened at their surfaces. Therefore, polycarbonates as the polymers other than ABS are mixed with ABS or elastomers to enable electroless plating. Such mixtures are commercially available as plating grades. However, polymer materials of such plating grades unavoidably tend to deteriorate in their physical properties such as decrease in heat resistance, as compared with their main components alone. Therefore, such polymer materials are hard to be used for molded products which are required to have heat resistance.

As an alternate method of such a chemical pre-treatment method, there hitherto has been proposed a surface-modifying method with the use of high-pressure carbon dioxide such as supercritical carbon dioxide or the like (cf. Patent Publication 1). Patent Publication 1 discloses a batch processing (i.e., a discontinuous treatment within a high-pressure vessel) in which a metal complex is dissolved in high-pressure carbon dioxide, and in which the high-pressure carbon dioxide having the metal complex dissolved therein is brought into contact with a polymer member, so as to allow the metal complex to penetrate into the surface of the polymer member.

Patent Publication 2 discloses the following method: that is, a metal complex allowed to penetrate into a polymer is reduced by heating, so that the metal complex is metalized and immobilized in the polymer, and this metal is caused to function as a catalyst nucleus for plating.

The present inventors already have disclosed the method for forming an electroless plating film with high adhesion to a polymer member, by using an electroless plating solution mixed with high-pressure carbon dioxide, after allowing a metal catalyst to penetrate into the polymer by the use of high-pressure carbon dioxide (Patent Publication 3). That is, the mixture of the electroless plating solution with the high-pressure carbon dioxide is allowed to penetrate into the polymer at such a low temperature as does not cause a plating reaction, and then, the temperature of the polymer is raised to a temperature at which a plating reaction can take place. According to the present inventors' studies, it is considered that a plating film with adhesion equal to or higher than a film obtained by the conventional etching method can be obtained, because the catalyst nucleus formed by thermal reduction of the metal complex is previously allowed to penetrate into the polymer, so that the electroless plating reaction can grow from the inner portion of the polymer by making use of this catalyst nucleus.

Patent Publication 1: JP-A-2001-316832

Patent Publication 2: JP-A-2007-56287

Patent Publication 3: Japanese Patent No. 3926835

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

As described above, the conventional plating method for resin molded products requires the pre-treatment which may burden the environment, and there is a limitation in selection of the kinds of the polymer materials.

When the method for surface-modifying the polymer member with the use of high-pressure carbon dioxide such as a supercritical fluid, according to Patent Publication 1, is employed to allow fine metal particles as a plating catalyst to penetrate into the polymer member by batch processing, the fine metal particles as the plating catalyst tend to be present on the surface portion of the polymer member after the thermal reduction of the fine metal particles.

In the meantime, as a result of the present inventors' studies, it has been found that the use of a metal complex containing a fluorine atom as a metal complex to be dissolved in high-pressure carbon dioxide is effective for the pre-treatment with the use of high-pressure carbon dioxide in a supercritical state. The metal complex containing a fluorine atom has a higher solubility in high-pressure carbon dioxide, so that it is possible to increase the concentration of the metal complex in a high-pressure vessel and to allow the metal complex to penetrate in a high concentration, which leads to reduction of the penetration-treating time. This will be described below in detail.

For example, the solubility of an acetylacetonatopalladium (II) complex, i.e., a metal complex containing no fluorine atom, in a high-pressure liquid carbon dioxide (under an atmosphere at a temperature of 40° C. and a pressure of 15 MPa) is several tens mg/L, which is a markedly low solubility. Therefore, 30 minutes to one hour or longer is required to allow this metal complex to penetrate into the polymer in a high concentration. Again, the thermal reduction of this metal complex requires a long time because of the high thermal stability of the metal complex. For the worse, the thermal reduction temperature is needed to be so high as 200° C. or higher.

In contrast, the solubility of a hexafluoro-acetylacetonatopalladium (II) complex, i.e., a metal complex containing a fluorine atom, in the same high-pressure carbon dioxide is several tens g/L, which is 100 times hither than the solubility of the former metal complex. Therefore, it is possible to increase the concentration of the metal complex in a high-pressure vessel in several minutes to several tens minutes, so that the penetration time becomes shorter than that for the former metal complex.

However, such a metal complex containing a fluorine atom is low in affinity to a polymer member, despite its markedly high solubility in high-pressure carbon dioxide. The metal complex having penetrated into the polymer disadvantageously returns to the high-pressure carbon dioxide side. Therefore, this metal complex can not be immobilized as one expected, only by allowing the metal complex to penetrate into the polymer, and thus, the concentration of the metal complex in the polymer is hard to increase.

As a result of the present inventors' studies in order to solve this problem, it becomes possible to increase the concentration of the metal complex in the polymer by the following method: the metal complex is allowed to penetrate into the polymer and is immediately subjected to a thermal reduction treatment in high-pressure carbon dioxide of a high temperature, to thereby increase the concentration of the metal complex in the polymer. The above-described metal complex containing a fluorine atom is low in thermal stability and thus can be thermally decomposed and reduced in perfect at a temperature of about 150° C.

However, the metal complex is hard to be immobilized in the polymer, if the thermal reduction is not carried out in the high-pressure vessel for use in penetration of the metal complex. The reasons therefor are described: firstly, the metal complex is high in affinity to carbon dioxide, and when carbon dioxide is discharged before the reduction treatment, the metal complex having penetrated into the polymer is also discharged together with the discharged carbon dioxide; and secondly, when the metal complex is allowed to penetrate into the polymer with the use of high-pressure carbon dioxide and the polymer is then taken out of the high-pressure vessel and is subjected to a thermal or chemical reduction treatment, the metal complex leaves the polymer before this treatment.

The present inventors have intensively studied the pre-treatment for plating by way of the batch processing with the use of this high-pressure vessel. As a result, they have revealed the following problems.

Firstly, when a plurality of polymer molded products are treated at once in a single high-temperature vessel, a metal complex tends to be thermally decomposed before it has penetrated into the polymers, so that some of the molded products have portions where the growth of plating films is poor and portions where the adhesion strength of the plating films is poor. That is, the molded products have variability in their qualilties.

Secondly, in case where the metal complex and carbon dioxide are allowed to penetrate into the polymer at a low temperature and then the temperature of the bath is raised to thermally decompose and reduce the metal complex in the polymer, the above-described variability in the qualities of the molded products can be suppressed, while the metal complex in the high-pressure vessel is not allowed to penetrate into the polymer molded products and is entirely decomposed together with an excess of the metal complex which does not penetrate into the polymer molded product but retains in the vessel, with the result that the expensive metal complex can not be recovered. In this regard, it is considered that a reducing agent such as an alcohol may be introduced under high pressure into the high-pressure vessel, instead of raising the inner temperature of the bath. However, also in this case, an excess of the metal complex which does not penetrate into the molded products can not be recovered. In this way, only a part of the metal complex fed into the high-pressure vessel is allowed to penetrate into the polymer molded products. The conventional reduction method is insufficient to recover the excess of the metal complex, and the metal complex is thermally decomposed or reduced in the vessel, which leads to a large loss, waste and significant hindrance in commercial production.

Thirdly, in case where the above-described electroless plating method with the use of high-pressure carbon dioxide is employed for the above-described pre-treatment for plating with the use of high-pressure carbon dioxide in a supercritical state, the following problem is found to arise. That is, the metal complex is allowed to penetrate into the molded products in the high-pressure vessel, and then, this metal complex is thermally reduced, metalized and immobilized in the molded products. In this case, the metal complex is reduced and immobilized from the surface of the resin molded product, so that the concentration of the fine metal particles or the metal complex becomes higher toward the surface layer of the resin molded product, as shown in FIG. 4(A). When a plating solution mixed with high-pressure carbon dioxide is allowed to penetrate into the polymer and a plating reaction is allowed to take place from the inner portion of the polymer, the catalytic activity of the surface layer of the polymer molded product becomes higher, which makes it hard to grow a plating film from the interior of the polymer. As schematically shown in FIG. 4(B), the penetration depth of the plating film becomes shallow on some sites of the molded product, and therefore, the adhesion strength of the plating film, although it is high, is variable in its value.

The present invention is developed in order to solve the foregoing problems. The first object of the present invention is to provide a method for allowing a metal complex to reliably penetrate into a polymer even by a low temperature treatment, and immobilizing the metal complex therein, by a batch processing for a pre-treatment for plating by which the metal complex is allowed to penetrate into the polymer, using high-pressure carbon dioxide, and to provide a method of pre-treatment for recovering an excess of the metal complex from the high-pressure vessel.

The second object of the present invention is to provide a method for improving and stabilizing an adhesion strength of a plating film in an electroless plating method with the use of high-pressure carbon dioxide, in which a plating reaction is caused in the polymer.

Means for Solving the Problems

The present invention includes the following preferred embodiments.

[1] A method for producing a composite material which contains a resin molded product, and this method is characterized by comprising the steps of

bringing a reducing agent into contact with the resin molded product to allow the reducing agent to penetrate into the resin molded product, and

bringing high-pressure carbon dioxide having an organic metal complex dissolved therein, into contact with the resin molded product into which the reducing agent has penetrated, to immobilize the organic metal complex in the resin molded product by the reducing agent.

[2] The method defined in the above item [1], wherein the reducing agent is removed from the surface layer of the resin molded product into which the reducing agent has penetrated, and then, the resin molded product is brought into contact with the high-pressure carbon dioxide having the organic metal complex dissolved therein.

[3] method defined in the above item [1], wherein the high-pressure carbon dioxide having the organic metal complex dissolved therein is brought into contact with the resin molded product under an atmosphere at a temperature lower than the thermal reduction temperature of the organic metal complex.

[4] The method defined in the above item [1], wherein a plating film is further formed on the resin molded product having the organic metal complex immobilized therein, by an electroless plating method with the use of high-pressure carbon dioxide.

[5] The method defined in the above item [3], wherein, after the organic metal complex is immobilized, the resin molded product is heated at a temperature higher than the thermal reduction temperature of the organic metal complex.

[6] method defined in the above item [5], wherein the treatment to heat the resin molded product at a temperature higher than the thermal reduction temperature of the organic metal complex is carried out after the organic metal complex is recovered from the reaction system.

[7] The method defined in the above item [5], wherein a plating film is further formed on the resin molded product by an electroless plating method with the use of high-pressure carbon dioxide, after the heat treatment at a temperature higher than the thermal reduction temperature of the organic metal complex.

[8] The method defined in the above item [1], wherein the reducing agent dissolved in a solvent is brought into contact with the resin molded product.

[9] The method defined in the above item [8], wherein the solvent contains high-pressure carbon dioxide.

[10] The method defined in the above item [8], wherein the solvent contains water or an alcohol.

[11] The method defined in the above item [1], wherein the organic metal complex contains a fluorine atom.

[12] The method defined in the above item [1], wherein the organic metal complex contains at least one metal element selected from Pd, Pt, Ni, Cu and Ag.

[13] The method defined in the above item [1], wherein the high-pressure carbon dioxide having the organic metal complex dissolved therein is in a supercritical state.

EFFECT OF THE INVENTION

Firstly, according to the present invention, in the batch processing for the pre-treatment for plating in which the metal complex is allowed to penetrate the polymer by the use of the high-pressure carbon dioxide, the metal complex can be allowed to reliably penetrate the polymer and can be immobilized therein by a treatment even at a low temperature; and an excess of the metal complex can be recovered from the high-pressure vessel. Secondly, according to the present invention, the adhesion strength of the resultant plating film can be improved and stabilized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the steps of forming a plating film in Examples.

FIG. 2 shows a schematic diagram of a high-pressure apparatus used in Examples.

FIG. 3 shows the steps of forming a plating film in Comparative Examples.

FIG. 4 shows the penetration state of fine metal particles and the formation of a plating film in Comparative Examples.

FIG. 5 shows the penetration state of fine metal particles and the formation of a plating film in Examples.

FIG. 6 schematically shows the distributions of the concentrations of the fine metal particles in Examples and Comparative Examples.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1: a resin material (or a resin molded product)     -   10: a high-pressure apparatus     -   11: a carbon dioxide bomb     -   13: a syringe pump     -   17: a second high-pressure vessel (or a high-pressure vessel)     -   20: a first high-pressure vessel     -   25: a separation recovering unit     -   26: a recovery tank     -   51: fine metal particles     -   52: a plating film     -   61: a reducing agent

BEST MODES FOR CARRYING OUT THE INVENTION

A method for producing a composite material containing a resin molded product, according to the present invention, is characterized by comprising the steps of

bringing a reducing agent into contact with the resin molded product so as to allow the reducing agent to penetrate into the resin molded product; and

bringing the resin molded product into which the reducing agent has penetrated, into contact with high-pressure carbon dioxide having an organic metal complex dissolved therein, to immobilize the organic metal complex in the resin molded product by the reducing agent.

In the present invention, the organic metal complex which has penetrated into the resin molded product is reduced with the reducing agent which has previously penetrated into the resin molded product, and is immobilized in the resin molded product. Therefore, it is not needed to heat the organic metal complex up to a temperature not lower than the thermal reduction temperature of the organic metal complex, in order to immobilize the organic metal complex in the resin molded product. That is, it is sufficient to bring the above-described high-pressure carbon dioxide having the organic metal complex dissolved therein, into contact with the above-described resin molded product under an atmosphere at a temperature lower than the thermal reduction temperature of the organic metal complex. In contrast, when the organic metal complex is immobilized by a thermal reduction reaction, it is needed to heat the resin molded product up to a temperature at which the thermal reduction reaction takes place, and to cool the resin molded product to a normal temperature, with the result that the throughput of the pre-treatment process is limited. For example, in case of a resin molded product shaped by injection molding, the resin molded product is caused to have a difference in residual stress between its skin layer and its inner portion while being shaped. Such a molded product, when heated and cooled, is likely to foam or crack at its surface or inside. According to the present invention, it becomes possible to solve these problems.

The resin molded product according to the present invention is not limited, and it may be an optionally shaped resin material. For example, the resin molded product is a resin material in the form of a sheet, pipe or fibers shaped by extrusion molding, injection molding or the like. The resin molded product in itself may be a final molded product or an intermediate product in the form of a sheet or the like to be fabricated later.

There is no particular limitation in selection of a resin material for the above-described resin molded product, and any of thermoplastic resins, thermosetting resins and photocurable resins may be used. The kind of a thermoplastic resin, if used, may be usually amorphous or crystalline, and it may be optionally selected. Specific examples thereof include polyolefins such as low-density polyethylene, high-density polyethylene, polypropylene and poly-4-methylpentene-1; polyvinyls such as polyvinyl chloride, polyvinyl alcohol and polyacrylonitrile; polyethers such as polyoxymethylene and polyethylene oxide; and other polymeric materials such as polyester, polyamide, polyimide, polymethyl methacrylate, polysulfone, polycarbonate and polylactic acid. Further examples thereof include aromatic polyesters such as polyethylene terephthalate; aromatic amides such as polyterephthalamide; and fluoropolymers such as polytetrafluoroethylene. Examples of the thermosetting resin include epoxy resins, phenol resins, polyimide, polyurethane, silicone resins, etc. Examples of the photocurable resin include photosensitive epoxy resins, photosensitive acrylic resins, photosensitive polyimide, etc. There may be used any of these resin materials which contains a filler such as glass fibers, carbon fibers, an inorganic compound, a ceramic or the like.

[Reducing Agent Penetration Step]

The method of the present invention firstly comprises a step of bringing a reducing agent into contact with the above-described resin molded product to thereby allow the reducing agent to penetrate into the resin molded product.

While the kind of the reducing agent to be used in the present invention may be optionally selected, there may be used, as the reducing agent, for example, dimethylamine borane, hydrazine, formaldehyde, sodium boron hydride, hypophosphorous acid, sodium hypophosphite or the like. Such a solid reducing agent, if used, is dissolved in a solvent such as water or an alcohol to prepare a solution thereof, and the resin molded product is immersed in this solution to thereby allow the reducing agent to penetrate into the resin. To improve the penetration of the reducing agent into the resin molded product, a ultrasonic wave may be applied to the solution, or the solution may be warmed, or the pH of the solution may be controlled in accordance with the kind of the reducing agent. For example, when sodium boron hydride is used as the reducing agent, desirably, a solution thereof is adjusted in pH to be alkaline. When sodium hypophosphite is used, desirably, a solution thereof is adjusted in pH to be neutral or acidic. When the reducing agent is used in the form of an aqueous solution thereof, a solvent with a low surface tension, such as ethanol, may be mixed with the aqueous solution, or an additive such as sodium lauryl sulfate may be dissolved in the aqueous solution, so as to decrease the surface tension of the aqueous solution and to facilitate the penetration thereof. This step may be carried out under stirring.

There is no limitation in selection of the solvent for use in dissolving of the reducing agent. For example, there may be used water; alcohols such as methanol, ethanol, isopropanol, butanol and ethylene glycol; ethers such as diethyl ether and tetrahydrofuran (THF); hexane; benzene; acetone; toluene; etc., among which water and alcohols such as ethanol are preferable. The concentration of the reducing agent to be dissolved in the solvent is not limited, and an optimal concentration thereof may be variable in accordance with the kinds of the reducing agent, the solvent and the resin into which the reducing agent penetrates. In an embodiment of the present invention, the concentration of the reducing agent is, for example, from 0.5 to 15% by weight, preferably from 1 to 10% by weight, when sodium hypophosphite is used as the reducing agent, and water, as the solvent.

There also may be used, as the reducing agent, an alcohol, polyalkylene glycol, phenol or the like, each having a hydroxyl group which exhibits a reducing action. Particularly, the use of ethanol is preferable, since ethanol is low in surface tension and is easy to penetrate into the resin. Examples of the alcohol include methanol, ethanol, isopropanol, butanol, ethylene glycol, 2-methoxyethanol, 2-ethoxyethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1,3-butanediol, etc. The use of a high molecular-weight polyalkylene glycol such as polyethylene glycol or the like is effective to inhibit the reducing agent from leaving the inner portion of the resin and to inhibit elimination of the effect of the reducing agent.

In the present invention, two or more selected from the above materials may be used in combination.

When the resin molded product is immersed in the reducing agent or the solvent containing the same to thereby allow the reducing agent to penetrate into the resin molded product, treating conditions such as a treating temperature (or a liquid temperature), a treating pressure, application or non-application of a ultrasonic wave, pH, etc. are not limited, and optimal conditions may be variable in accordance with the kinds of the reducing agent, the solvent and the resin material.

In an embodiment of the present invention, the treating temperature (or the liquid temperature) is, for example, from 30 to 150° C., preferably from 60 to 100° C.; and the pH of the reducing agent or the solvent containing the reducing agent is, for example, from 3 to 11, preferably from 5 to 9.

Preferably, this step is carried out under an atmospheric of a normal pressure, from the viewpoint of productivity, etc. The normal pressure herein referred to means a non-pressurized atmosphere.

Again, in the present invention, the reducing agent or the solution thereof in the solvent is mixed with (or dissolved in) a high-pressure fluid to thereby improve the penetration of the reducing agent. The use of high-pressure carbon dioxide or carbon dioxide in a super-critical state (hereinafter optionally referred to as “supercritical carbon dioxide”) as the high-pressure fluid is particularly effective to swell the surface of the resin and to allow the reducing agent to deeply penetrate into the resin.

In the present invention, “high-pressure carbon dioxide” means not only supercritical carbon dioxide but also a liquid carbon dioxide and a carbon dioxide gas, obtained by highly pressurizing carbon dioxide. For example, there is given a carbon dioxide gas formed under a pressure of 5 MPa or higher, preferably 7.1 MPa or higher, at 20° C. or higher, preferably 31° C. or higher.

While there is no limitation in selection of the upper limits of the temperature and pressure of the high-pressure carbon dioxide, the upper limits thereof may be determined by the capability of a reaction vessel to be used. For example, in case of the high-pressure vessel used in Examples, the use of high-pressure carbon dioxide with a temperature of 200° C. or lower and a pressure of 30 MPa or lower is desirable.

In this regard, carbon dioxide is put in a supercritical state at 31° C. or higher under a pressure of 7.1 MPa or higher.

The treatment to allow the reducing agent to penetrate into the resin molded product by the use of high-pressure carbon dioxide is conducted as follows: for example, the resin molded product is immersed in the reducing agent or the solution thereof in the solvent in the high-pressure vessel; and then, the high-pressure vessel is filled with high-pressure carbon dioxide. In this case, it is considered that the high-pressure carbon dioxide swells the resin molded product, which makes it possible for the solution containing the reducing agent to penetrate into the resin molded product.

A temperature for the treatment with the use of the high-pressure carbon dioxide is, for example, from 20 to 200° C., preferably from 31 to 100° C.; and a pressure therefor is, for example, from 5 to 30 MPa, preferably from 7.1 to 20 MPa.

A treating time for the reducing agent penetration step is not limited, and a time during which the reducing agent can sufficiently penetrate into the resin molded product is enough for this treating time. An optimal treating time may be variable according to the kinds of the reducing agent, the solvent therefor and the resin material, the treating temperature, the treating pressure and application or non-application of a ultrasonic wave. In an embodiment of the present invention, the treating time is, for example, from 3 minutes to 3 hours, preferably from 15 minutes to 1.5 hours.

This step may be carried out under stirring.

[Organic Metal Complex-Immobilization Step]

The method of the present invention includes a step of bringing the above-described resin molded product into which the reducing agent has penetrated, into contact with high-pressure carbon dioxide having the above-described organic metal complex dissolved therein, thereby immobilizing the organic metal complex in the resin molded product by the above-described reducing agent.

Preferable as the organic metal complex to be used in the present invention is a material which contains at least one metal element selected from Pd, Pt, Ni, Cu and Ag, any of which has a certain solubility in high-pressure carbon dioxide and functions as a plating catalyst. Examples of the organic metal complex include bis(cyclopentadienyl)nickel, bis(acetylacetonato)palladium (II), dimethyl(cyclooctadienyl)platinum (II), hexafluoroacetylacetonatopalladium (II), hexafluoroacetylacetonatohydrate copper (II), hexafluoroacetylacetonatoplatinum (II), hexafluoroacetylacetonato(trimethylphosphine)silver (I), dimethyl(heptafluorooctanedionate)silver (AgFOD), etc.

Among the above-described organic metal complexes, an organic metal complex containing a fluorine atom, that is, an organic metal complex having a fluorine atom at its ligand, is preferable in the present invention. The organic metal complex containing a fluorine atom is well dissolved in carbon dioxide and thus can be dissolved in high-pressure carbon dioxide at a high concentration and is then brought into contact with the resin molded product. The organic metal complex containing a fluorine atom is hard to penetrate into the resin molded product. However, a high concentration of the organic metal complex can be allowed to penetrate into the resin molded product and can be efficiently immobilized in the resin molded product, because the reducing agent has previously penetrated into the resin molded product.

In this step, desirably, the high-pressure carbon dioxide and the organic metal complex are formed into a homogeneous phase by using a stirrer or the like.

Again, in this step, supercritical carbon dioxide may be preferably used as the high-pressure carbon dioxide.

A treating temperature and a treating pressure in this step are not limited, and an optimal treating temperature and an optimal treating pressure may be variable according to the kinds of the organic metal complex and the resin molded product, the treating time, etc. In an embodiment of the present invention, the treating temperature is, for example, from 20 to 200° C., preferably from 31 to 100° C.; and the treating pressure is, for example, from 5 to 30 MPa, preferably from 7.1 to 20 MPa.

Again, the treating temperature and the treating pressure in this step desirably should satisfy the supercritical conditions for carbon dioxide (31° C. or higher and 7.1 MPa or higher), and the treating temperature should not allow the organic metal complex to be thermally reduced. Under such conditions, if in a supercritical state, the organic metal complex decreases in its surface tension and thus becomes easy to penetrate into the resin molded product. Since the temperature does not allow the organic metal complex to be thermally reduced, the organic metal complex which does not penetrate into the resin molded product and remains in the reaction system is not decomposed and thus can be recovered and recycled. Further, it becomes possible to prevent the concentration of the organic metal complex or the fine particles of the reduced metal from increasing in the proximity of the surface of the resin molded product, so that the metal complex or the fine metal particles can more deeply penetrate into the resin molded product. Consequently, it can be expected that the adhesion strength of the resultant plating film will be improved, as will be described later.

The upper limits of the treating temperature and the treating pressure may be selected in accordance with the capability of the reaction vessel to be used. For example, in case of the high-pressure vessel used in Examples, desirably, the treating temperature and the treating pressure should be 200° C. or lower and 30 MPa or lower, respectively, in order to ensure the tight sealing of the reaction vessel.

The thermal reduction temperature of the organic metal complex in the present invention indicates a temperature to which the organic metal complex is heated to be thermally reduced. That is, the thermal reduction temperature is the same as a temperature at which the organic metal complex starts to thermally decompose.

The organic metal complex decomposes when thermally reduced, so that the metal atoms are liberated. The organic metal complex is a polymer, and the metal atoms which are liberated in the polymer are instable, with the result that several metal atoms collect to form a cluster so as to be stabilized. On the other hand, the ligand forming the organic metal complex is dissolved in supercritical carbon dioxide and thus is not immobilized in the resin molded product, leaving the resin molded product during a degassing operation.

In this regard, the thermal reduction temperature (or the thermal decomposition-starting temperature) of the organic metal complex in the present invention is defined as a temperature at which the mass of the organic metal complex starts to decrease, when measured with a differential scanning calorimeter (DSC).

In the present invention, desirably, the treating temperature in this step is controlled to a temperature 10° C. or more higher than the thermal decomposition-starting temperature of the organic metal complex in an air or a nitrogen atmosphere, wherein the thermal decomposition-starting temperature of the organic metal complex is previously measured with a differential scanning calorimeter (DSC). When the heat resistant temperature of the organic metal complex is high, desirably, the organic metal complex is subjected to a high-pressure treatment under an atmosphere at such a temperature that the reducing agent previously having penetrated into the resin molded product does not deteriorate, sublime or boil. For example, when hexafluoroacetylacetonatopalladium (II) is used as the organic metal complex, the treating temperature may be set at 63° C. or lower, for example, 50° C., since the thermal decomposition-starting temperature of this metal complex is about 73° C. or higher under a nitrogen atmosphere.

The treating time in this step is not limited, so long as the organic metal complex can sufficiently penetrate into the resin molded product. An optimal treating time may be variable according to the kinds of the organic metal complex and the resin molded product, the treating temperature, the treating pressure, etc. In an embodiment of the present invention, the treating time is, for example, from 5 minutes to 3 hours, preferably from 15 minutes to 1.5 hours.

In this step, the concentration of the organic metal complex in the high-pressure carbon dioxide is not limited. An optimal concentration of the organic metal complex may be variable according to the kind of the organic metal complex, etc. In an embodiment of the present invention, the concentration of the organic metal complex is, for example, 100 mg/L or more, preferably 1,000 mg/L or more. Again, the upper limit of the concentration of the organic metal complex is not limited, and the upper limit thereof may be a saturated concentration of the organic metal complex relative to the high-pressure carbon dioxide.

In the method of the present invention, the resin molded product into which the reducing agent has penetrated may be brought into contact with the above-described high-pressure carbon dioxide having the organic metal complex dissolved therein, after the reducing agent has been removed from the surface layer of the resin molded product. By this treatment, the reducing agent not only simply penetrates into the resin molded product, but also, the reducing agent penetrates into the resin molded product while the reducing agent in the surface layer of the resin molded product is removed. Therefore, the organic metal complex can be immobilized at portions deeper inside from the surface layer of the resin molded product. Consequently, the metal complex can be allowed to reliably penetrate into the polymer and can be immobilized by the treatment at a relatively low temperature.

In this regard, the surface layer herein referred to means, for example, a surface portion with a depth of 50 mm or less from the surface of the resin molded product. Within this range of depth, a plating film is formed, when the resin molded product is brought into contact with the organic metal complex without removing the reducing agent and is further subjected to an electroless plating. This plating film as a whole is poor in adhesion to the resin molded product, having variability in its adhesion degree to every site of the resin molded product.

The removal of the reducing agent from the surface layer of the resin molded product may be confirmed based on a decrease in the amount of the organic metal complex which has penetrated into, at least, the surface layer of the resin molded product. Desirably, the organic metal complex which has penetrated into the surface layer of the resin molded product is decreased so that the amount (or concentration) of the residual organic metal complex in the surface layer can be smaller than that in a deeper site of the resin molded product, or so that the amount (or concentration) of the organic metal complex per a predetermined depth unit can be maximal (or a peak) at a deeper site of the resin molded product than the surface layer thereof.

This is described in detail. By positively removing the reducing agent from the surface layer of the resin molded product, the reduction reaction of the metal complex selectively takes place only at the inner portion of the resin molded product, and the metal complex is immobilized therein. Because of the low concentration of the reducing agent in the surface layer of the resin molded product, the metal complex is hard to be reduced in the surface layer, while the metal complex is easily reduced in the inner portion of the resin molded product where the concentration of the reducing agent is higher. As a result, the concentration of the dispersed metal complex in the inner portion of the resin molded product becomes higher than that in the surface layer thereof. For this reason, as will be described later, a plating film is hard to grow at the surface layer of the resin molded product, and the plating film is easy to reliably grow in the inner portion thereof, when a plating reaction is allowed to take place in the inner portion of the resin molded product by electroless plating with the use of high-pressure carbon dioxide. Therefore, the adhesion and stability of the resultant plating film is improved.

The treatment for removing the reducing agent from the surface layer of the resin molded product is made, for example, by rinsing the resin molded product into which the reducing agent has penetrated, with water within a predetermined time, or by blowing an air onto the same resin molded product within a predetermined time. By doing so, the reducing agent can be removed from the surface layer of the resin molded product. That is, a part of the reducing agent which has penetrated into the resin molded product can be removed. Particularly when the reducing agent is an alcohol or the like which is easy to volatilize, such a reducing agent can be removed from the surface layer of the resin molded product, only by exposing the resin molded product to an air within a predetermined time.

[Thermal Reduction Step for Organic Metal Complex]

Again, in the method of the present invention, the above-described resin molded product may be further heated at a temperature higher than the thermal reduction temperature of the organic metal complex, after the organic metal complex has been immobilized, and before an electroless plating treatment as will be described later. When the resin molded product is heated at a temperature higher than the thermal reduction temperature of the organic metal complex after the immobilization of the organic metal complex in the deep site of the resin molded product inside the surface layer thereof as described above, the organic metal complex moves toward the side of the surface, so that the concentration of the organic metal complex can be increased in the deep site inside the surface layer of the resin molded product. Accordingly, the amount of the catalyst nuclei in the deep site of the resin molded product inside the surface layer thereof is increased, in comparison with the amount of the catalyst nuclei in the just previous step without the pre-treatment (or an anneal treatment) by heating. As a result, the adhesion degree of the resultant plating film to the resin molded product further can be improved. Since the organic metal complex is present at a higher concentration in a site with a predetermined depth in the resin molded product, the plating film can stably grow from this predetermined depth, and thus, stability in the adhesion degree of this plating film can be further improved.

Why the adhesion of the plating film is improved by this heat treatment is not clearly known. However, the following mechanism is considered to work. In case where an electroless plating film is grown from the inner portion of a resin molded product of a thermoplastic resin or the like by the use of high-pressure carbon dioxide, it is known that a depth of from 50 to 200 nm or less, more preferably from 50 to about 100 nm, is appropriate for a plating solution to penetrate into the resin molded product. It is considered that too large a plating solution penetration depth increases the swelling of the uppermost surface of the resin molded product and increases a stress thereto, which leads to a decrease in the strength of the resin molded product. Therefore, the penetration depth of the metal complex or the fine metal particles is appropriately from 50 to 200 nm from the surface of the resin molded product. However, in some of actual penetration treatments, the metal complex or the fine metal particles tend to penetrate into the resin molded product to a depth of 1 μm or more.

It is considered that, by the heat treatment under such a situation, the fine metal particles which deeply penetrate into the resin molded product and which are incompatible with the resin molded product collect on a region with an appropriate depth in the inner portion in the proximity of the surface of the resin molded product, and that such collection of the fine metal particles may contribute to improvement of a plating reactivity in the inner portion of the resin molded product. It is also considered that there may remain the metal complex which deeply penetrates into the resin molded product, since this metal complex is not reacted with the reducing agent and is not discharged from the surface of the resin molded product, together with the discharge of the high-pressure carbon dioxide under reduced pressure, thus remaining in the deep site of the resin molded product. In either case, it is considered that the metal complex tends to bleed out to the surface of the molded product by the thermal reduction treatment, and therefore that the fine metal particles tend to collect at a region with an appropriate depth in the proximity of the surface of the resin molded product.

A treating temperature for this heat treatment is not limited, so long as this temperature is higher than the thermal reduction temperature for the organic metal complex to be used. For example, when hexafluoroacetylacetonato-palladium (II) of which the thermal decomposition-starting temperature is 73° C. is used as the organic metal complex, the treating temperature is, for example, 73° C. or higher, preferably 100° C. or higher. The upper limit of the treating temperature may be variable according to the kind of the resin, since the resin molded product tends to deform when the treating temperature is far higher than the glass transition temperature (Tg) of the resin.

A treating time for the heat treatment is not limited, as long as the thermal reduction of the organic metal complex can be sufficiently carried out. An optimal treating time may be variable according to the kind of the organic metal complex to be used, the treating temperature, etc. In an embodiment of the present invention, the treating time is, for example, from 0.5 to 100 hours, preferably from 1 to 50 hours.

In the method of the present invention, the treatment for heating the resin molded product having the organic metal complex immobilized therein, up to a temperature higher than the thermal reduction temperature of the organic metal complex is preferably carried out after the organic metal complex has been recovered from the reaction system. By doing so, the organic metal complex which does not penetrate into the resin molded product can be recovered as it is, in a non-reduced state. The recovered organic metal complex may be recycled.

[Plating Film-Forming Step]

In the method of the present invention, an electroless plating method with the use of high-pressure carbon dioxide may be further employed to form a plating film on the resin molded product having the organic metal complex immobilized therein, or on the resin molded product after the heat treatment thereof at a temperature higher than the thermal reduction temperature of the organic metal complex.

In this regard, the electroless plating method herein referred to means a method for depositing a metal film in the proximity of the surface of a substrate having a catalytic activity, by using a reducing agent, without using an external electric supply.

When the electroless plating method with the use of high-pressure carbon dioxide is employed, a plating film is grown from the organic metal complex immobilized at a deep site inside the surface layer of the resin molded product, so that the resultant plating film is adhered to the resin molded product with a high adhesion. In addition, no plating film is grown from the surface layer of the resin molded product, since the organic metal complex is absent or a little in amount if present, on the surface layer of the resin molded product. Therefore, the adhesion of the plating film is kept stable at a high value.

In contrast, for example, when a plating film is formed on a resin molded product to which an organic metal complex is simply added, by the electroless plating method with the use of high-pressure carbon dioxide, the temperature of the resin molded product is raised from the surface thereof toward the inside thereof with a temperature gradient kept, and a plating film is grown from the organic metal complex present at a high concentration in the surface layer of the resin molded product, since the organic metal complex is present at a higher concentration on the surface of the resin molded product than the inner portion thereof. Therefore, the adhesion of the plating film to the resin molded product can not be improved. The surface layer of the resin molded product includes a portion where the plating film is grown from a site on the surface and a portion where the plating film is grown from a site on the inner portion of the surface, so that the plating film has portions with lower adhesion, and this adhesion is instable.

In the electroless plating method with the use of high-pressure carbon dioxide, according to the present invention, there may be used any of the known electroless plating solutions for use in the electroless plating methods: for example, an acidic electroless plating solution such as a Ni—P plating solution (e.g., Nicoron DK, etc. manufactured by OKUNO CHEMICAL INDUSTIRES CO., LTD.) or the like may be used. The use of a plating solution reactive with a neutral or alkaline substance is unsuitable, since such a plating solution is oxidized with high-pressure carbon dioxide.

The above-described electroless plating solution optionally may be diluted with water or an alcohol for use. While the electroless plating solution contains water as a main component, an alcohol may be mixed therewith to make it easy to stably mix the plating solution with high-pressure carbon dioxide. The surface tension of the electroless plating solution admixed with an alcohol becomes markedly lower because of the lower surface tension of the alcohol than water, so that the plating solution is easier to penetrate into the resin molded product. In general, to prepare an electroless plating solution, a stock solution for the electroless plating solution is diluted with water in a component ratio recommended by a manufacturer. Further mixing of an alcohol with water in an optional ratio makes it possible to prepare a stable electroless plating solution which is uniformlay compatible with high-pressure carbon dioxide. While a volume ratio of an alcohol to water may be optionally selected, it is preferable to add 10 to 80% of the alcohol relative to water, from the viewpoint of the stability of the electroless plating solution.

The alcohol for use in the electroless plating solution may be optionally selected. For example, there are given methanol, ethernol, n-propanol, isopropanol, butanol, heptanol, ethylene glycol, diethylene glycol, 2-methoxyethanol, 2-ethoxyethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, n,n-butanediol, tert-butylalcohol, 2-(2-ethoxyethoxy)ethanol, 1-propoxy-2-propanol, 2(2-methoxypropoxy)propanol, 2(2-butoxyethoxy)ethanol, 3-methoxy-1-butanol, 2-methyl-2,4-pentanediol, etc., among which ethanol, 2-methoxyethanol and 1,3-butanediol are preferable.

The electroless plating solution may contain publicly known additives. For example, the electroless plating solution may contain a complexing agent which forms a stable soluble complex with a metal ion in the electroless plating solution, such as citric acid, acetic acid, succinic acid, lactic acid or the like. Again, the electroless plating solution may contain a stabilizer such as a sulfur compound (e.g., a thiourea, etc.), lead ion, a brightener or a wetting agent (or a surfactant).

In this step, as the high-pressure carbon dioxide, supercritical carbon dioxide (with a temperature of 31° C. or higher and with a pressure of 7.1 MPa or higher) is preferably used.

Preferably, a treating temperature and a treating pressure for this step are so controlled as to satisfy critical conditions for carbon dioxide and to cause formation of a plating film. In particular, an optimal treating temperature may be variable according to the kind of the plating solution to be used.

In an embodiment of the present invention, the treating temperature is, for example, from 50 to 95° C., preferably from 70 to 90° C., and the treating pressure is, for example, from 5 to 30 MPa, preferably from 7.1 to 20 MPa.

There is no limitation in selection of the treating time in this step, so long as a plating film can be sufficiently formed on the resin molded product. An optimal treating time may be variable according to the kind of the electroless plating solution, the treating temperature, the treating pressure, etc. In an embodiment of the present invention, the treating time is, for example, from 5 minutes to 3 hours, preferably from 15 minutes to 1.5 hours.

Again, this step may be carried out under stirring.

EXAMPLES

Hereinafter, Examples of the method for producing a composite material containing the resin molded product of the present invention will be described in detail, while the scope of the present invention is not limited to the following Examples in any way.

Example 1

In this Example, a predetermined high-pressure apparatus was used in a pre-treatment for plating, so as to dissolve a reducing agent and an organic metal complex in a high-pressure fluid and to bring the resulting solution into contact with a resin material. In this Example, carbon dioxide was used as the high-pressure fluid. Firstly, the high-pressure apparatus used in this Example will be described.

FIG. 2 shows a schematic diagram of the high-pressure apparatus 10 for use in the pre-treatment for plating and electroless plating according to the embodiment of the present invention.

As shown in FIG. 2, the high-pressure apparatus 10 includes a first high-pressure vessel 20 for holding a resin material (or a resin molded product) 1; a liquid carbon dioxide bomb 11 for storing carbon dioxide to be fed to the first high-pressure vessel 20; a syringe pump 13 for pressurizing carbon dioxide; a second high-pressure vessel 17 for storing an organic metal complex; a separation-recovering unit 25 for separating and recovering the organic metal complex dissolved in high-pressure carbon dioxide; and a recovery container 26 for receiving the recovered organic metal complex. Again, as seen in FIG. 2, there are disposed, at appropriate sites among the respective constitutive elements of the high-pressure apparatus 10, valves 12, 16, 18, 19 and 27, pressure gauges 14 and 22, a check valve 15 and a back pressure valve 24, for use in control of a pressure and flowing of the high-pressure carbon dioxide.

The first high-pressure vessel 20 can be cooled by a cartridge heater (not shown) and a cooling circuit (not shown), and the vessel 20 has a strength high enough to withstand a high pressure from a supercritical carbon dioxide. The second high-pressure vessel 17 also has a strength high enough to withstand the high pressure from the supercritical carbon dioxide.

Accordingly, it is possible to feed, to the first high-pressure vessel 20, a solvent mixture of a reducing agent or a solvent containing the reducing agent with high-pressure carbon dioxide, and a solvent mixture of the organic metal complex with high-pressure carbon dioxide. Again, the first high-pressure vessel 20 may be filled with an electroless plating solution.

In this Example, as the reducing agent, there was used a solvent mixture of ethylene glycol with ethanol; as the resin material 1, there was used a substrate of 70 mm in length, 15 mm in width and 1 mm in thickness, which was formed of polyamide 6 (PA6) mixed with 10% of glass fibers; and as the organic metal complex, there was used hexafluoroacetylacetonatopalladium (II) containing a plating catalyst Pd. A nickel-phosphorus film as a plating film was formed by electroless plating with the use of high-pressure carbon dioxide, and a nickel film was further formed on this film by electrolytic plating.

In this Example, this plating film was formed on the surface of the resin material 1, following the steps shown in FIG. 1.

Firstly, a liquid mixture of ethanol (100 mL) with ethylene glycol (100 mL) was prepared and was charged together with the resin material 1 into the first high-pressure vessel 20 with an inner volume of 300 mL. The first high-pressure vessel 20 was controlled in temperature at 80° C. in a sealed state. Next, a liquid carbon dioxide fed from the liquid carbon dioxide bomb 11 was pressurized with the syringe pump (260D manufactured by ISCO) 13 until the pressure gauge 14 indicated 15 MPa. Thus, supercritical carbon dioxide was provided. Then, the manual needle valve 19 was opened through the check valve 15 to raise the inner pressure of the first high-pressure vessel 20 up to 15 MPa, to thereby fill the first high-pressure vessel 20 with the supercritical carbon dioxide. The manual needle valve 19 was closed after the pressure had been raised. The inner pressure of the first high-pressure vessel 20 was maintained for 60 minutes during which the supercritical carbon dioxide was brought into contact with the resin material 1 so as to allow ethanol and ethylene glycol to penetrate into the resin material 1 (Step S21 on FIG. 1).

Next, the manual needle valve 23 was opened, and the back pressure valve 24 was also opened, to open the first high-pressure vessel 20 to an air. Next, the resin material 1 and the solvent mixture of ethanol with ethylene glycol were removed from the first high-pressure vessel 20; the resin material 1 was washed with water and was then dried at a normal temperature in an air until ethanol and ethylene glycol adhered to the surface of the resin material 1 was vaporized. Thus, out of the reducing agent which had penetrated into the resin material 1, the reducing agent in the surface layer (or a site on the uppermost surface) of the resin material 1 could be removed from the resin material 1.

Next, the dried resin material 1 was charged in the first high-pressure vessel 20, and the first high-pressure vessel 20 was then sealed, while the organic metal complex (100 mg) was charged in the second high-pressure vessel 17 with an inner volume of 100 mL, and the second high-pressure vessel 17 was then sealed and controlled at 50° C. Next, the liquid carbon dioxide fed from the liquid carbon dioxide bomb 11 was pressurized with the syringe pump 13 until the pressure gauge 14 indicated 15 MPa. Thus, supercritical carbon dioxide was provided. Next, the manual needle valve 16 was opened through the check valve 15, and the inner pressure of the second high-pressure vessel 17 was raised to 15 MPa to thereby dissolve the organic metal complex in the supercritical carbon dioxide. Next, the manual needle valve 18 was opened, and the supercritical carbon dioxide containing the organic metal complex was brought into contact with the resin material 1 for 45 minutes to thereby allow the organic metal complex to penetrate into the resin material 1 (Step S22 on FIG. 1)

In this Example, the solvent mixture in the first high-pressure vessel 20 was always stirred with a stirrer 21.

The inner temperature of the first high-pressure vessel 20 which included the metal complex dissolved in the high-pressure carbon dioxide so as to be brought into contact with the resin material 1 was set at 50° C. This temperature was 10° C. or more lower than a thermal decomposition-starting temperature of about 73° C. or higher of hexafluoroacetyl-acetonatopalladium (II) used as the organic metal complex under a nitrogen atmosphere.

After the organic metal complex had penetrated into the resin material 1, the manual needle valve 23 was opened, and the back pressure valve 24 was further opened to thereby open the first high-pressure vessel 20 to an air through the separation-recovering unit 25, and then, the resin material 1 was taken out. The organic metal complex separated from the carbon dioxide was recovered in the recovery container 26. The amount of the recovered metal complex is shown in Table 1 below.

In this Example, after the organic metal complex had penetrated into the resin material 1, the resin material 1 into which the catalyst penetrated was subjected to a heat treatment at 150° C. in an air for one hour. Thus, the resin material 1 used in this Example was pre-treated for plating as described above.

Next, an electroless plating film was formed on the pre-treated resin material 1 (Step S23 on FIG. 1). In this Example, as a stock solution for an electroless plating solution, there was used Nicoron DK manufactured by OKUNO CHEMICAL INDUSTRIES CO., LTD., which contained a metal salt of nickel sulfate, a reducing agent and a complexing agent. In this Example, the electroless plating solution was mixed with water and ethanol.

In the plating film-forming step, firstly, the resin material 1 and the above-described Ni—P electroless plating solution were charged and sealed in the first high-pressure vessel 20 shown in FIG. 2. The temperatures of the first high-pressure vessel 20 and the Ni—P electroless plating solution were controlled at 50° C. which was lower than a plating reaction temperature (from 70 to 85° C.) Under these conditions, no plating film was grown on the surface of the resin material 1, since the resin material 1 was in contact with the electroless plating solution of a temperature lower than the plating reaction temperature (at which no plating reaction took place).

Next, high-pressure carbon dioxide was introduced into the first high-pressure vessel 20 controlled at the low temperature which permitted no plating reaction. In this Example, supercritical carbon dioxide was used as the high-pressure carbon dioxide. Concretely, the liquid carbon dioxide fed from the liquid carbon dioxide bomb 11 was pressurized with the syringe pump 13 (260D manufactured by ISCO) until the pressure gauge 14 indicated 15 MPa, to provide the supercritical carbon dioxide. The manual needle valve 19 was opened through the check valve 15 to raise the inner pressure of the first high-pressure vessel 20 up to 15 MPa, to thereby fill the first high-pressure vessel 20 with the supercritical carbon dioxide, which was then brought into contact with the resin material 1.

Next, the temperature of the first high-pressure vessel 20 was raised to 85° C. to cause a plating reaction in the first high-pressure vessel 20. As a result, an electroless plating reaction took place on the surface of the resin material 1 to form a plating film. According to this plating film-forming method, the electroless plating solution had penetrated into the fine metal particles present in the inner portion of the resin material 1 as described above, and therefore, the plating film was grown by using the fine metal particles as catalyst nuclei, which were present not only in the surface of the resin material 1 but also in the inner portion thereof. That is, in the plating film-forming method of this Example, the plating film was grown in the inner portion with a free volume of the resin material 1, so that the plating film with high adhesion could be formed while being deeply rooted into the inner portion of the resin material 1.

After completion of the plating, the manual needle valve 23 was opened, and the back pressure valve 24 was opened, to discharge the carbon dioxide from the first high-pressure vessel 20. Then, the first high-pressure vessel 20 was opened to take out the resin material 1 therefrom. Next, the resin material 1 taken out of the first high-pressure vessel 20 was dried for a while, so as to be degassed to remove the carbon dioxide and the electroless plating solution from the inner portion of the resin material 1.

Next, the resin material 1 was subjected to electroless plating and electrolytic plating under a normal pressure (Step S24 on FIG. 1). Firstly, the oxidized surface of the plating film on the resin material 1 was activated with hydrochloric acid. After that, a conventional electroless nickel-phosphorus plating solution was used in an air for electroless plating under a normal pressure, to thereby deposit a plating film with a thickness of 1 μm on the resin material. Then, a conventional electrolytic plating method was employed in an air to deposit a nickel film with a thickness of 40 μm by using as an electrode the plating film formed by the electroless plating method. Thus, the entire surface of the resin material 1 was coated with a metal film by the above-described method.

Comparative Example 1

In this Comparative Example, a plating film was formed on the surface of a resin material 1 by the steps shown in FIG. 3. In this Comparative Example, a reducing agent was brought into contact with the resin material 1, but the step of allowing the reducing agent to penetrate into the resin material (Step S21 on FIG. 1) was not carried out. The plating film was formed on the surface of the resin material 1 in the same manners as in Example 1, except for this point.

However, the plating film was hardly formed on the resin material 1 in a step of carrying out electroless plating with the use of high-pressure carbon dioxide (Step S32 on FIG. 3). This is considered as follows: because of the low compatibility of the metal complex to the resin material, the metal complex, although once penetrated into the resin material, was discharged simultaneously with the discharge of the high-pressure carbon dioxide, and thus, most of the metal complex could not be retained in the resin material 1.

Comparative Example 2

In this Comparative Example, supercritical carbon dioxide in which an organic metal complex containing a plating catalyst was dissolved was brought into contact with a resin material 1, and the temperature of the high-pressure vessel 20 for use in penetration was set at 150° C. Except for these, a plating film was formed on the surface of the resin material 1 by the same treatment as in Comparative Example 1. Thus, the entire surface of the resin material 1 was coated with a metal film.

Example 2

In this Example, a plating film was formed on a resin material 1 by the same steps shown in FIG. 1, as well as Example 1. However, the heat treatment carried out in Example 1 was omitted, after the treatment (Step S22 on FIG. 1) wherein supercritical carbon dioxide in which an organic metal complex containing a plating catalyst was dissolved was brought into contact with the resin material 1 to allow the supercritical carbon dioxide to penetrate into the resin material; and instead, the resin material 1 was dried in an air at a normal temperature for one hour. After that, plating films were formed (Steps S23 and S24 on FIG. 1). Thus, the entire surface of the resin material 1 was coated with a metal film.

Example 3

In this Example, a plating film was formed on a resin material 1 by the steps shown in FIG. 1, as well as Example 1. However, the step of bringing a reducing agent into contact with a resin material to allow the reducing agent to penetrate into the resin material (Step S21 on FIG. 1) was carried out in an air without using the high-pressure apparatus shown in FIG. 2. In concrete, the resin material 1 was charged in a sealed vessel (not shown) containing a mixture of ethanol (100 mL) with ethylene glycol (100 mL), which was then subjected to a ultrasonic wave at 80° C. under a normal pressure for 60 minutes; and then, the resin material 1 was taken out and was dried until ethanol and ethylene glycol on the surface thereof were vaporized. Except for these, plating films were formed on the resin material 1 in the same manners as in Example 1 (Steps S22 to S24 on FIG. 1). Thus, the entire surface of the resin material 1 was coated with a metal film.

Example 4

In this Example, a plating film was formed on the surface of a resin material by the same method as in Example 3. However, instead of the mixture of ethanol (100 mL) with ethylene glycol (100 mL), a solution of sodium hypophosphite (500 mg) in ethanol (100 mL) and water (100 mL) was used. Thus, the entire surface of the resin material 1 was coated with a metal film.

Example 5

In this Example, a plating film was formed on the surface of a resin material 1 by the same steps shown in FIG. 1, as well as Example 3. However, instead of the mixture of ethanol (100 mL) with ethylene glycol (100 mL), a mixture of 2-methoxyethanol (90 mL), water (90 mL) and hypophosphorous acid (20 mL) was used. Except for these, the entire surface of the resin material 1 was coated with a metal film in the same manner as in Example 3.

Example 6

In this Example, a plating film was formed on the surface of a resin material 1 by the same steps shown in FIG. 1, as well as Example 1. However, ethanol was used as a reducing agent in the step of bringing the reducing agent into contact with the resin material 1 to thereby allow the reducing agent to penetrate into the resin material (Step S21 on FIG. 1). The ethanol (10 mL) was charged in the second high-pressure vessel 17 set at 80° C. to form a gaseous mixture of supercritical carbon dioxide with the ethanol by opening the manual needle valve 16 while the manual needle valve 19 being closed. After that, the manual needle valve 18 was opened to feed this gaseous mixture into the first high-pressure vessel 20 including the resin material 1, so as to bring the gaseous mixture into contact with the resin material 1. Except for these, the plating films were formed on the resin material 1 in the same manner as in Example 1 (Steps S22 to S24 on FIG. 1). Thus, the entire surface of the resin material 1 was coated with a metal film.

The qualities of the plating films of Examples 1 to 6 and Comparative Examples 1 and 2 were evaluated. As the items for quality evaluation, an environmental test and evaluation of adhesion were conducted. As conditions for the environmental test, the temperature and humidity were set at 80° C. and 80%, respectively; the time was set at 100 hours; and each 10 plated resin materials were used. The evaluation of adhesion was conducted as follows: the tensile strengths of each 10 plated resin materials were measured with a tensile tester (AGS-J 100N manufactured by SHIMADZU CORPORATION) (according to JIS H8630). The results thereof are shown in Table 1, together with the evaluation of the external appearances of the plating films and the amounts of the recovered organic metal complexes. The tensile strengths are shown as the minimum values, maximum values and average values of each 10 plated resin materials. In this regard, the target value for a tensile strength of a plating film with the use of an ABS resin by the conventional etching method was 10 N/cm or higher.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 C. Ex. 1 C. Ex. 2 External ◯ ◯ ◯ ◯ ◯ ◯ X ◯ appearance Environmental ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ — Δ test Tensile Minimum 18-25 10-15 14-21 17-23 19-27 12-19 — 6-20 strength Maximum [N/cm] Average 21 12 17 20 23 15 — 12 Amount of recovered 71 75 73 70 74 73 85  0 organic metal complex [mg] (charged amount: 100 mg) External Appearance: ◯ means that a plating film was formed without any problem and without any defect in its external appearance. Δ means that a plating film was formed without any problem, however, peeling or swelling was observed in a part of the plating film. X means that a plating film was incomplete in some portions thereof, or no plating film was formed. Environmental Test: ⊚ means that, after the test, no peeling or swelling was observed in all of 10 plating films. Δ means that, after the test, swelling was observed in one or more plating films, however, no peeling was observed in all of the plating films. X means that, after the test, peeling and swelling were observed in one or more plating films.

It was known from the results of Table 1 that the plating films formed in Examples 1 to 6 had sufficient adhesion strengths with quite no problem in practical use thereof. On the other hand, the plating film of Comparative Example 1 was not successfully formed, since the step of bringing the reducing agent into contact with the resin material 1 so as to allow the reducing agent to penetrate into the resin material 1 (Step S21 on FIG. 1) was not carried out. It is known from this fact that, because of the reducing agent allowed to penetrate into the resin material 1, the organic metal complex was reduced to form fine metal particles which functioned as the plating catalyst nuclei and were immobilized in the resin material 1, in each of Examples 1 to 6.

As compared with the plating film formed by the conventional method in Comparative Example 2, the variabilities in the tensile strengths of the plating films formed in Examples 1 to 6 were found to be smaller, and their average values were found to be larger. Again in comparison with Comparative Example 2 wherein quite no organic metal complex could be recovered, the organic metal complexes could be recovered in Examples 1 to 6.

This is considered as follows. In Comparative Example 2, the organic metal complex was allowed to penetrate into the resin material 1 by the thermal reduction and was immobilized in the resin material 1, in the first high-pressure vessel 20. Therefore, as shown in FIG. 4(A), the concentration of the fine metal particles or the metal complex 51 became higher toward the uppermost surface of the resin material 1, with the result that, as shown in FIG. 4(B), the catalytic activity was higher at the uppermost surface thereof, and the plating film was hard to grow from the inner portion of the resin material 1, when the plating solution mixed with the high-pressure carbon dioxide was allowed to penetrate into the resin material 1 and then the plating reaction was caused from the inner portion of the resin material 1. In FIG. 4, numeral 51 refers to the fine metal particles or the metal complex; and numeral 52, to the plating film.

On the other hand, in each of Examples 1 to 6, the organic metal complex 51 was allowed to penetrate into the resin material 1 in the first high-pressure vessel 20, at a temperature at which the organic metal complex 51 was not thermally reduced, and then, the organic metal complex 51 was reduced with the reducing agent 61 which had previously penetrated into the resin material, and thus was metalized and immobilized in the resin material, as shown in FIG. 5(A). Therefore, as shown in FIG. 5(B), the concentration of the fine metal particles or the metal complex 51 was higher in a deep site away from the surface of the resin material, as compared with the conventional method. Therefore, the plating film 52 was grown from the inner portion of the resin material 1, as shown in FIG. 5(C), in comparison with the conventional method, when the plating solution mixed with the high-pressure carbon dioxide was allowed to penetrate into the resin material 1 so as to cause the plating reaction. Consequently, the adhesion strength of the plating film was improved, and variability in the adhesion strength was smaller.

The adhesion strength of the plating film of Example 1 which had been subjected to the heat treatment as follows was known to be higher than that of Example 2 from the results of Table 1: after the supercritical carbon dioxide in which the organic metal complex containing the plating catalyst had been dissolved was brought into contact with the resin material 1 and was allowed to penetrate into the resin material 1, the thermoplastic resin into which the catalyst penetrated was subjected to the heat treatment at 150° C. in an air for one hour in Example 1, while such a thermoplastic resin was not subjected to any heat treatment but was dried at a normal temperature in an air for one hour in Example 2. It could be understood from this fact that the steps of bringing the supercritical carbon dioxide in which the organic metal complex containing the plating catalyst had been dissolved, into contact with the resin material, so as to allow such supercritical carbon dioxide to penetrate into the resin material 1, and then carrying out the additional reduction treatment (or the thermal reduction in Example 1) are effective to improve the adhesion strength of the plating film.

FIG. 6, consisting of FIGS. 6(A), 6(B) and 6(C), shows the graphs which quantitatively illustrate the distributions of the concentrations of the fine metal particles in the resin materials 1, respectively. FIG. 6(A) shows the distribution of the concentrations of the fine metal particles in Comparative Example 2, wherein the distributions of the concentration of the fine metal particles was maximum at the surface layer of the resin material. In this case, the plating solution was present at a high density on the surface layer and was grown by the use of the activated fine metal particles as the catalyst nuclei, so that the plating film as shown in FIG. 4(B) was formed. In contrast, FIG. 6(B) shows the distribution of the concentrations of the fine metal particles found when the metal complex was allowed to penetrate after the reducing agent had been removed from the surface layer of the resin material, and it was found that the distributions of the concentration of the fine metal particles was maximum at a deeper site than the surface layer thereof. In this case, the plating solution was allowed to more deeply penetrate into the resin material from the surface layer thereof, and was grown from such fine metal particles, so that the plating film as shown in FIG. 5(C) was formed.

FIG. 6(C) shows the distribution of the concentrations of the fine metal particles found when the metal complex was allowed to penetrate after the reducing agent was removed from the surface layer of the resin material, and when such a resin material was further subjected to the heat treatment. The concentration of the fine metal particles was maximum at a deeper site than the surface layer thereof, as well as that shown in FIG. 6(B). In addition, the fine metal particles were decreased in number at the deep site, and the fine metal particles were increased in number at a deep portion where the concentration of the fine metal particles was maximum, as compared with FIG. 6(B). Therefore, the plating film shown in FIG. 6(C) was grown from far more fine metal particles present at an appropriate depth, as compared with the plating film shown in FIG. 6(B), so that the adhesion strength of this plating film was improved.

INDUSTRIAL APPLICABILITY

According to the method for producing the composite material containing the resin molded product of the present invention, a plating film with a higher adhesion strength and with stability in the high adhesion strength can be formed on the resin molded product. When such a plating film is formed with the use of high-pressure carbon dioxide by a batch processing, this method can be preferably employed in order to improve the production stability and the quality of plating films and to achieve lower running cost. 

1. A method for producing a composite material containing a resin molded product, said method being characterized by comprising the steps of bringing a reducing agent into contact with said resin molded product to allow said reducing agent to penetrate into said resin molded product, and bringing high-pressure carbon dioxide having an organic metal complex dissolved therein, into contact with said resin molded product into which said reducing agent had penetrated, so as to immobilize said organic metal complex in said resin molded product by said reducing agent.
 2. The method according to claim 1, wherein said reducing agent is removed from the surface layer of said resin molded product into which said reducing agent had penetrated, and then, said resin molded product is brought into contact with said high-pressure carbon dioxide having said organic metal complex dissolved therein.
 3. The method according to claim 1, wherein said high-pressure carbon dioxide having said organic metal complex dissolved therein is brought into contact with said resin molded product under an atmosphere at a temperature lower than a thermal reduction temperature of said organic metal complex.
 4. The method according to claim 1, wherein a plating film is further formed on said resin molded product having said organic metal complex immobilized therein, by an electroless plating method with the use of high-pressure carbon dioxide.
 5. The method according to claim 3, wherein, after the immobilization of said organic metal complex, said resin molded product is further heated at a temperature higher than the thermal reduction temperature of said organic metal complex.
 6. The method according to claim 5, wherein said treatment for heating said resin molded product at the temperature higher than the thermal reduction temperature of said organic metal complex is carried out after said organic metal complex has been recovered from a reaction system.
 7. The method according to claim 5, wherein, after said treatment for heating said resin molded product at the temperature higher than the thermal reduction temperature of said organic metal complex, a plating film is further formed on said resin molded product by an electroless plating method with the use of high-pressure carbon dioxide.
 8. The method according to claim 1, wherein said reducing agent is dissolved in a solvent and is then brought into contact with said resin molded product.
 9. The method according to claim 8, wherein said solvent contains high-pressure carbon dioxide.
 10. The method according to claim 8, wherein said solvent contains water or an alcohol.
 11. The method according to claim 1, wherein said organic metal complex contains a fluorine atom.
 12. The method according to claim 1, wherein said organic metal complex contains at least one metal element selected from Pd, Pt, Ni, Cu and Ag.
 13. The method according to claim 1, wherein said high-pressure carbon dioxide in which said organic metal complex is dissolved is in a supercritical state. 